Electron beam devices, in particular a scanning electron microscope (also referred to as SEM below) and/or a transmission electron microscope (also referred to as TEM below), are used to examine objects (also referred to as samples) in order to obtain knowledge in respect of the properties and behavior of the objects under certain conditions.
In an SEM, an electron beam (also referred to as primary electron beam below) is generated using a beam generator and focused on an object to be examined using a beam guiding system. An objective lens is used for focusing purposes. The primary electron beam is guided over a surface of the object to be examined by way of a deflection device. This is also referred to as scanning. The area scanned by the primary electron beam is also referred to as scanning region. Here, the electrons of the primary electron beam interact with the object to be examined. Interaction particles and/or interaction radiation result as a consequence of the interaction. By way of example, the interaction particles are electrons. In particular, electrons are emitted by the object—the so-called secondary electrons—and electrons of the primary electron beam are scattered back—the so-called backscattered electrons. The interaction particles form the so-called secondary particle beam and are detected by at least one particle detector. The particle detector generates detection signals which are used to generate an image of the object. An image of the object to be examined is thus obtained. By way of example, the interaction radiation is X-ray radiation or cathodoluminescence. At least one radiation detector is used to detect the interaction radiation. Additionally or alternatively, electrons of the primary electron beam are used to ablate or modify the object, as explained further below.
In the case of a TEM, a primary electron beam is likewise generated using a beam generator and directed onto an object to be examined using a beam guiding system. The primary electron beam passes through the object to be examined. When the primary electron beam passes through the object to be examined, the electrons of the primary electron beam interact with the material of the object to be examined. The electrons passing through the object to be examined are imaged onto a luminescent screen or onto a detector—for example in the form of a camera—by a system comprising an objective. By way of example, the aforementioned system additionally also may comprise a projection lens. Here, imaging may also take place in the scanning mode of a TEM. Such a TEM is often referred to as STEM. Additionally, provision may be made for detecting electrons scattered back at the object to be examined and/or secondary electrons emitted by the object to be examined using at least one further detector in order to image the object to be examined. Additionally or alternatively, in a TEM or STEM, electrons of the primary electron beam are used to ablate or modify the object, as explained further below.
Combining the functions of an STEM and an SEM in a single particle beam device is known. It is therefore possible to carry out examinations of objects with an SEM function and/or with an STEM function using this particle beam device.
Moreover, a particle beam device in the form of an ion beam column is known. Ions used for processing an object are generated using an ion beam generator arranged in the ion beam column. By way of example, material of the object is ablated or material is applied onto the object during the processing. The ions are additionally or alternatively used for imaging.
Furthermore, the prior art has disclosed the practice of analyzing and/or processing an object in a particle beam device using, on one hand, electrons and, on the other hand, ions. By way of example, an electron beam column having the function of an SEM is arranged at the particle beam device. Additionally, an ion beam column, as explained above, is arranged at the particle beam device. The electron beam column with the SEM function serves, in particular, for examining further the processed or unprocessed object, but also for processing the object.
An object may be imaged with a high spatial resolution using an electron beam device. In particular, this is achieved by a very small diameter of the primary electron beam in the plane of the object. Further, the spatial resolution may improve the higher the electrons of the primary electron beam are initially accelerated in the electron beam device and decelerated to a desired energy (referred to as landing energy) at the end of the objective lens or in the region of the objective lens and the object. By way of example, the electrons of the primary electron beam are accelerated using an acceleration voltage of 2 kV to 30 kV and guided through an electron column of the electron beam device. The electrons of the primary electron beam are only decelerated to the desired landing energy, with which they are incident on the object, in the region between the objective lens and the object. By way of example, the landing energy of the electrons in the primary electron beam lies in the range between 10 eV and 30 keV.
There are objects which, on account of their structure, may only be expediently examined in an electron beam device if the electrons in the primary electron beam incident on these objects only have a low landing energy, for example an energy of less than 100 eV. Electrons with such low energy for example ensure that these specific objects are not destroyed and/or do not charge upon irradiation by electrons. Further, electrons at such low energy levels are particularly suitable for obtaining an image with a high surface sensitivity (i.e. a particularly good information content in respect of the topography and/or the material of the surface of the object) of an object to be examined.
When generating an image of the object, the user of an electron beam device always strives to obtain the ideal image quality of an image of the object which is required for examining an object. Expressed differently, a user always wishes to create an image of the object with such a high image quality that they are able to analyze the object to be examined well on account of the image and the image information contained therein. Here, the image quality may be determined by means of e.g. objective criteria. By way of example, the image quality of an image becomes better with increasing resolution in the image or with increasing contrast, for example depending on different materials. Alternatively, the image quality may be determined on the basis of subjective criteria. Here, a user determines individually as to whether or not an obtained image quality is sufficient. However, what may by all means occur in this case is that the image quality deemed sufficient by a first user is not considered sufficient by a second user. By way of example, the image quality of an image of an object may also be determined on the basis of the signal-to-noise ratio of the detector signal. The image quality is not sufficiently good in the case of a signal-to-noise ratio in the range from 0 to 5. By way of example, if the signal-to-noise ratio lies in the range from 20 to 40, this is referred to as a good signal-to-noise ratio (and hence also a good and sufficient image quality).
As mentioned above, it is also possible to detect interaction radiation, for example cathodoluminescence and X-ray radiation. When detecting interaction radiation, a user of an electron beam device may by all means seek to obtain the quality of the representation of the detection signals of a radiation detector based on the detected interaction radiation which is required for examining an object. By way of example, if X-ray radiation is detected by the radiation detector, the quality of the representation is determined e.g. by a good detection signal of the radiation detector. By way of example, the latter is embodied as an EDX detector. By way of example, the quality of the representation is then influenced by the count rate of the detected X-ray quanta on one hand and, on the other hand, by the full width at half maximum of the measured peaks in the X-ray spectrum. The quality of the representation of the detection signals increases with a higher count rate and a smaller full width at half maximum. By way of example, if cathodoluminescence is detected by a radiation detector, the quality of the representation may likewise be determined e.g. by a good detection signal of the radiation detector. By way of example, the quality of the representation is determined by the count rate of the detected photons of the cathodoluminescence. The count rate may be influenced by a suitable optical unit for light. Further, the primary electron beam may be set in such a way that the object emits as many photons as possible overall or as many photons as possible within a specific wavelength interval.
In order to obtain a good image quality of an image and/or a good representation of the detection signals based on the detected interaction radiation, which image and/or representation is/are generated using an electron beam device, a user of an electron beam device known from the prior art selects a desired landing energy with which the electrons are incident on the object. Moreover, a user selects an area of the object, which area is examined by scanning the primary electron beam over the area. For example, the area is selected by moving a sample stage holding the object within an object chamber of the electron beam device. Moreover, the user may select settings of further control parameters of at least one control unit. By way of example, the control parameters are physical variables, in particular a control current or a control voltage, but also e.g. the ratio of physical variables, in particular an amplification of physical variables. The values of the physical variables are adjustable at the control units or using the control units and these control and/or feed the units of the electron beam device in such a way that desired physical effects, for example, the generation of specific magnetic fields and/or electrostatic fields, are brought about.
The control parameters can be e.g. as follows.
A first control parameter of a first control unit sets the contrast in the generated image. In principle, the contrast is the brightness difference (i.e. the intensity difference) between the brightest pixel with a maximum luminance Lmax and the darkest pixel with a minimum luminance Lmin in an image. A smaller brightness difference between the two pixels means a low contrast. A larger brightness difference between the two pixels means a high contrast. By way of example, the contrast may be specified as Weber contrast or as Michelson contrast. Here, the following applies for the Weber contrast:
                              K          W                =                                                            L                max                                            L                min                                      -                          1              ⁢                                                          ⁢              with              ⁢                                                          ⁢              0                                ≤                      K            W                    ≤          ∞                                    [        1        ]            
The following applies for the Michelson contrast:
                              K          M                =                                                                              L                  max                                -                                  L                  min                                                                              L                  max                                +                                  L                  min                                                      ⁢                                                  ⁢            with            ⁢                                                  ⁢            0                    ≤                      K            M                    ≤          1                                    [        2        ]            
The contrast which is substantially generated by the secondary electrons is determined by the topography of the surface of the object. On the other hand, the contrast which is substantially generated by the backscattered electrons is substantially determined by the material of the imaged object region. It is also referred to as material contrast. The material contrast depends on the mean atomic number of the imaged region of the object. By way of example, the contrast increases when a higher gain factor is set at an amplifier of the detector, wherein the detector is used to detect the secondary electrons and/or backscattered electrons. The amplifier amplifies the detection signal generated by the detector. Analogously, the contrast e.g. decreases when a smaller gain factor is set at the amplifier of the detector.
A second control parameter of a second control unit sets the brightness in the generated image. In principle, the brightness in an image is related to each pixel in the image. A first pixel with a higher brightness value than a second pixel appears brighter in the image than the second pixel. By way of example, the brightness is set by setting a gain factor of the detection signal of the detector. Here, the brightness of each pixel in the image is increased or lowered by an identical amount, for example also using a color table stored in a memory unit, with a specific brightness corresponding to a color included in the color table.
A third control parameter of a third control unit serves e.g. for actuating the objective lens, the latter being used to set the focusing of the primary electron beam onto the object.
A fourth control parameter for actuating a fourth control unit serves to center the primary electron beam in the objective lens. By way of example, the fourth control unit serves to set electrostatic and/or magnetic units of the electron beam device, by means of which the centering of the primary electron beam in the objective lens is set.
Moreover, the image quality of an image of the object and/or the quality of the representation of the detection signals based on the detected interaction radiation is/are influenced by a fifth control parameter of a fifth control unit for controlling and setting electrostatic and/or magnetic deflection units which are used in the electron beam device for a so-called “beam shift”. As a result of this, it is possible to set the position of the scanning region and optionally displace the scanning region to a desired position. This may occur without the use of the sample stage (also referred to as object holder below), on which the object is arranged. By way of example, if the scanning region migrates out of the actual region of the object observed using the electron beam device on account of a change in the settings on the electron beam device, the primary electron beam is displaced in such a way as a result of translational movements in the case of a “beam shift” that the scanning region once again lies in the desired observed region.
A stigmator used in an electron beam device may also influence the image quality of the image of the object and/or the quality of the representation of the detection signals based on the detected interaction radiation. The stigmator—a magnetic and/or electrostatic multi-pole element—is used, in particular, for correcting an astigmatism. The stigmator may be set by a sixth control unit using a sixth control parameter.
The image quality of an image of the object and/or the quality of the representation of the detection signals based on the detected interaction radiation may, however, also be influenced by the position of a mechanically displaceable unit of the electron beam device. By way of example, the image quality is influenced by the position of an aperture which is used to shape and delimit the primary electron beam in the electron beam device.
The image quality of an image of the object and/or the quality of the representation of the detection signals based on the detected interaction radiation may further be influenced by the so-called scan rotation. This is a rotation of the scanning region in the plane of the scanning region about an optical axis of the electron beam device.
The image quality of an image of the object and/or the quality of the representation of the detection signals based on the detected interaction radiation may further be influenced by a beam blank system. The beam blank system is a deflection system deflecting a primary particle beam in such a way that the primary particle beam does not impinge the object.
Among many other parameters not mentioned here, all of the aforementioned control parameters influence imaging, analyzing and/or processing together. Therefore, an image of the object obtained by the particle beam device is based on several control parameters. Each control parameter may be controlled and set using its associated control unit. For example, at least one of the aforementioned control units is an interface controlled by a user, in particular a keyboard, a touchscreen and/or a slider. Moreover, at least one of the aforementioned control units may be used for controlling and setting at least two control parameters. For example, a single control unit may be used to control and set a first control parameter first. A second control parameter is controlled and set using the single control unit after the first control parameter is controlled and set.
It is known that an image of the object may be provided using different detectors, each detector being controlled by a different control unit using a different control parameter. In other words, the aforementioned image shown on the monitor may be provided using the signals of those different detectors. If a user wants to change the control parameter of a specific detector, the user has to manually identify the specific detector, for example by clicking on a specific area of the content shown in the monitor of the particle beam device and changing the value of the control parameter of this specific detector. However, on one hand, this is rather laborious. On the other hand, this is rather error-prone since a user often changes a control parameter of a detector which the user actually does not want to change since the user has identified a wrong detector.
It is therefore desirable to be able to provide a method and a particle beam device for carrying out the method, by means of which values of control parameters for control units for actuating components of a particle beam device are easy to change and/or by means of which a change of control parameters is not as error-prone as in the prior art.